Gas turbines are widely used in commercial operations for power generation. A gas turbine typically includes a compressor located at the front, one or more combustors around the middle, and a turbine at the rear. The compressor can include multiple stages of compressor blades attached to a rotor. Ambient air, as a working fluid, enters an inlet of the compressor, and rotation of the compressor blades progressively compresses the working fluid. The compressor can include one or more variable blade rows, such as inlet guide vanes (IGVs) and variable stator vanes (VSVs), which can be used to control the flow of ambient air into the compressor.
Some of the compressed working fluid is extracted from the compressor through extraction ports for other use, and the remainder of the working fluid exits the compressor and flows to the combustors. The working fluid mixes with fuel in the combustors, and the mixture ignites to generate combustion gases having a high temperature, pressure, and velocity. The combustion gases exit the combustors and flow to the turbine where they expand to produce work.
Electricity demand typically increases with increases in ambient temperature. Maximizing output of gas turbines at times with increased ambient temperatures is advantageous because of commercial opportunities for significant revenue generation as electricity demand and prices escalate with the ambient temperature. However, the capacity to supply electricity with gas turbines generally decreases as the ambient temperature increases. This is due to the negative influence of increased ambient temperature on density and airflow capacity of the turbine. Thus, for typical gas turbines, increased ambient temperature provides for increased economic opportunity with reduced capacity to fulfill energy demands.
Power generation revenues can also be enhanced by providing electrical power grid frequency stabilization services. For instance, if demand exceeds capacity—due to, for example, too many HVAC units running, the electrical grid can experience an “under-frequency” event. The need for frequency stabilization services has increased due to the rising contribution of renewable sources of energy connected to the grid. In particular, intermittent sources of energy, such as wind turbines and solar panels, can contribute to a transient excess of power applied to the grid, resulting in an “over-frequency” event. For instance, a wind turbine can provide a transient excess of power to the grid due to an increase in wind at the wind turbine site. A photovoltaic array can provide a transient excess of power to the grid as the sun comes out and solar rays are incident on the photovoltaic array. Such transient excess supplies of power can result in over-frequency events. Conversely, as renewable sources of power diminish due to, for instance, low wind speeds or on a cloudy day, an “under-frequency” event can occur, particularly in situations where generation demand exceeds the capacity of assets connected to the grid.
Gas turbines can be operated to provide frequency stabilization services by providing more or less output power to the grid. For instance, gas turbines can be operated to output more power to the grid in response to an under-frequency event. Alternatively, gas turbines can be operated to output less power to the grid in response to an over-frequency event.
The rotational speed of gas turbines is not a parameter that can be adjusted to provide frequency stabilization for the grid. The rotational speed of the gas turbines is synchronized to the frequency of the grid. For instance, the nominal rotational speed for 50 Hz grids is about 3000 RPM, and for 60 Hz grids is about 3600 RPM. To provide frequency stabilization, the output power of gas turbines is typically increased using techniques such as wet compression, automatic over-firing, and adjustment of variable blade rows according to variable blade row schedules that compensate for flow needs without user select-ability. These techniques do not typically provide the user the flexibility to control the output of the gas turbine to provide optimum output for revenue generation.
Thus, a need exists for a system and method that provides flexibility to an operator to control the gas turbine to provide enhanced output for increased revenue generation, or alternatively, to operate the gas turbine to provide frequency stabilization services. A system and method that can reduce the effects of increased ambient temperature on gas turbine output would be particularly useful.